It's the Swedish bakers dozen so you can eat 3 raw eggs + shells on the way home and still have a dozen eggs to put in the fridge. It takes three eggs to equal the calories found in a small donut which is why the bakers dozen eggs is 15 instead of 13.
In Singapore, chicken eggs come in packs of 6, 10, 12 (always labelled as having two bonus eggs: 10 + 2), 15, and 30. Duck eggs come in packs of 6. Quail eggs come in cans (NFI how many they include).
Come to Japan: 1,2,4,6, and 10 are the common ones (10 is most common at supermarkets). They have flats as well at some stores which I'm guessing are 30 but I don't remember.